Field of the Invention
The present invention relates to flip chip mounting of elements, and more particularly to a resin sealing structure for elements, such as acoustic surface wave elements and GaAs elements, whose electric characteristics are changed by any foreign matter sticking to the surface.
Flip chip mounting of elements according to the prior art is accomplished by forming bumps on pads on the surface of elements, and connecting those bumps to pads on the substrate side. After the flip chip mounting, the gap between each element and the substrate is sealed with resin to ease stress, prevent the invasion of foreign matter and protect the bumps. However, if any foreign matter sticks to the surface of a GaAs element or a surface acoustic wave element, which is operable at a high frequency, the desired electric characteristics cannot be obtained, and therefore the gap between the substrate and the element should have an airtight structure, with the element covered with resin all around.
To meet this requirement, a structure in which the gaps between the substrate and the elements are made airtight is formed by dropping a resin of high viscosity type, which would not enter into the gaps between the substrate and the elements, on the elements and hardening it.
For instance, in an example described in Paper A380 presented at the 1995 Convention of the Institute of Electronics, Information and Communication Engineers, after bumps are formed on semiconductors, the heights of bumps are made uniform, an electroconductive adhesive is transcribed on them, and the semiconductors are flip chip-mounted into cavities in the substrate. After that, insulating resin is applied around the elements and, after the resin is hardened, solder sealing is formed with metallic caps.
However, in a structure wherein flip chip-mounted elements are covered with resin as in this example, since the resin enters through the gaps between the substrate and the elements to come into contact with the electrode pattern, signals often cannot flow, resulting in a failure to achieve the desired characteristics.
Moreover, a structure using insulating resin or metallic caps involves many constituent parts and many manhours spent to fit them, resulting in poor productivity and impossibility to supply inexpensive products.